gearset. Three multiple-disk clutches-one sprag, one roller clutch, and two bands - provide the reaction elements required to obtain the desired function of the compound planetary gearset.

The torque converter smoothly couples the engine to the planetary gear through oil and hydraulically y provides additional torque mulitplication when required. The torque converter consists of a pump (driving member), a turbine (driven member), and a reaction member, known as a stator.

The compound planetary gearset gives three foward ratios and one reverse. Changing of the gear ratios is fully automatic in relation to vehicle speed and load.

Planetary Gears

Planetary gears are used in the Hydra-Matic 400 transmission as a basic means of multiplying the torque from the engine. The name is derived from the physical arrangement of the gears. They are always in mesh and thus cannot "clash" like other gears that go in and out of mesh. The gears are so designed so several teeth are in mesh or in contact at one time. This distributes the forces over several teeth at one time for greater strength. Because the shafts generally used with planetary gear trains can be arranged on the same centerline, a compact system can be obtained.

A planetary gear train consists of a center or sun gear, an internal or ring gear, and a planetary carrier assembly which includes and supports the smaller planet gears or pinions (fig. 7-12). A planetary gearset can be used to increase speed increase torque, reverse the direction of rotation, or function as a coupling for direct drive. Increasing the torque is known as operating in reduction because there is always a decrease in the speed of the output member proportional to the increase in the output of torque. This means that with a constant input speed, the output torque increases as the output speed decreases.

Reduction can be obtained in several ways. In a simple reduction, the sun gear is held stationary, and the power is applied to the internal gear in a clockwise direction. The planetary pinions rotate in a clockwise direction and "walk" around the stationary sun gear, thus rotating the carrier assembly clockwise in reduction (fig. 7-13).

Direct drive results when any two members of the planetary gear train rotate in the same direction at the same speed. In this condition, the pinions do not rotate on their pins but act as wedges to lock the entire unit together as one rotating assembly.

To obtain reverse, restrain the carrier from turning freely and power is applied to either the sun or the internal gear. This causes the planet pinions to act as idlers, thus driving the output member in the opposite

Figure 7-12. - Planetary gearset.